Document Prisma Client singleton pattern

Added documentation for Prisma Client singleton pattern and configuration.

patterns/prisma-client.md

@@ -1,3 +1,8 @@
+# Patroon: Prisma Client singleton
+
+## lib/prisma.ts
+
+```ts
 import { PrismaClient } from '@prisma/client'
 
 const globalForPrisma = globalThis as unknown as { prisma: PrismaClient | undefined }
@@ -7,3 +12,16 @@ export const prisma = globalForPrisma.prisma ?? new PrismaClient({
 })
 
 if (process.env.NODE_ENV !== 'production') globalForPrisma.prisma = prisma
+```
+
+## prisma.config.ts (Prisma v7 vereiste)
+
+```ts
+import 'dotenv/config'
+import { defineConfig } from 'prisma/config'
+
+export default defineConfig({
+  schema: 'prisma/schema.prisma',
+  migrations: { path: 'prisma/migrations' },
+})
+```